crypto: crc32-generic - use unaligned access macros when needed

crc32-generic doesn't have a cra_alignmask set, which is desired as its
->update() works with any alignment.  However, it incorrectly assumes
4-byte alignment in ->setkey() and when outputting the final digest.

Fix this by using the unaligned access macros in those cases.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>